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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old October 12th, 2008, 14:31   #1
Jimbo70
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Angry 16785 - EGR System: Insufficient Flow

I thought the timing issue was going to be the stickier wicket, but it isn't. I cannot solve the CEL I'm getting for a 16785 - EGR System: Insufficient Flow. Now before you send me to the Wiki or the FAQ, I've been there and:

- Replaced the EGR last year because it was plugged solid.
- Had the rest of the intake cleaned, again because it was plugged.
- Recalibrated the EGR in adaptation per the instructions in the FAQ.
- Replaced the MAF... twice. First time with a Pierburg, then after reading the FAQ with a Bosch unit.
- Reset the EGR calibration to the factory setting thinking that was causing the insufficient flow issue.
- Inspected all the vacuum hoses.

All I have to show for this is a (probably) good spare MAF, a clean EGR and a CEL.

What would my next step be?

Jim
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Old October 12th, 2008, 15:08   #2
DanG144
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Jimbo,
Take a log of the MAF data, from an idle to 4000 rpm or so, going through the gears at full throttle.
look for a basic setting button for a MAF data block, and use the basic setting test to grab another log.
Graph your logs, and see if that will help make a call.
Dan
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Old October 12th, 2008, 15:58   #3
Jimbo70
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Quote:
Originally Posted by DanG144
Jimbo,
Take a log of the MAF data, from an idle to 4000 rpm or so, going through the gears at full throttle.
look for a basic setting button for a MAF data block, and use the basic setting test to grab another log.
Graph your logs, and see if that will help make a call.
Dan
Will do.
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Old October 13th, 2008, 19:06   #4
Jimbo70
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Thanks to Office 2007, making charts isn't as intuitive as it used to be. That being said, here is my MAF chart:


After listening to the car while going through the gears, it sounded to me like it was slow to build boost, then slow to let the boost go on decel. Here is a chart of the manifold pressure and MAF versus atmospheric pressure:


This second boost chart is a sample of a larger log. With the exception of 160.06 seconds, where I shifted, I was at full throttle the entire log. Seems to me something isn't kosher here.

Jim
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Old October 14th, 2008, 09:56   #5
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Here is another log, charted using Excel 2003. A much more intuitive program.
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Old October 14th, 2008, 16:28   #6
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Jim,
That does look a bit suspicious.
The 400 actual MAF when you have 250 specified is about what you would get if your EGR valve was closed. What was your N18 duty cycle doing at that time? It was logged also, wasn't it? From your earlier posts, it seemed you were expecting to have the EGR opening?
It might be worth making a graph of MAP specified vs actual as well. I don't see why your MAP would die off at higher RPM, then spike upwards again.

Did you find the basic setting test for the EGR/MAF? A log of that could help, too.

Dan
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Old October 14th, 2008, 19:20   #7
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I have all that information... on my thumb drive at work where I have Office 2003 that is so much easier to graph with. I'll post those tomorrow. That being said I wouldn't expect a relatively new (and really clean) EGR to stick. It moves when a vacuum pump is used.

Jim
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Old October 15th, 2008, 06:35   #8
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Here you go, with the EGR duty cycle.

Thanks,
Jim
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Old October 15th, 2008, 08:09   #9
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and the MAP data? specified and actual on the same profile? Or a full throttle run from idle, through the gears to as fast you care to go, taking RPM up to 4k or so.
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Old October 15th, 2008, 10:29   #10
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I hope I'm getting this right. These two charts come from the same 12 second full throttle pull. You will see one dip at the very beginning from a shift.

Chart 1 is the EGR and MAF


Chart 2 is the MAF again but with atmospheric pressure and boost.


What my untrained eye is seeing is that my boost is all over the place under full throttle. Wouldn't that normally be a steady curve up to the point where of maximum allowable boost? Could it be an issue with the N75 valve?
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Old October 15th, 2008, 13:04   #11
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N75 or turbine vane controls.

But we really should see SPECIFIED MAP as well as ACTUAL MAP.

Please look for another group that has RPM, specified MAP, actual MAP and N75 duty cycle.

Any luck on basic settings test for the EGR? There should be one for the N75/turbine charge pressure control, too.

Dan
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Old October 15th, 2008, 16:38   #12
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Thanks again Dan. I will look for this the nxt time I have a moment, probably this weekend.
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Old October 19th, 2008, 12:12   #13
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My tentative diagnosis is a bad N75 valve, and without posting more charts here is why:

- I hooked up the VAG-COMM to my '03 Golf TDI and started looking at basic settings at idle. While idling the EGR cycles on and off. As this happens you can watch the corresponding mg/R number go up and down as the EGR cycles (I thought it was the MAF number, but I don't have the data in front of me). You can also hear a "click" while the engine is idling that corresponds with the indicator in the basic settings changing from EGR On to EGR Off and back.

- With my wife's car, however, although the indicator in the basic settings says that the EGR is turning on and off, the corresponding mg/R number does not change, nor is there the clicking noise as the valve cycles. I traced and inspected the vacuum lines going from the the EGR to the N75 and from the N75 to wherever those lines go, and they appear to be in good shape.

Before I sink another $70 or so into a piece I think I need, can anyone think of anything else that would cause what I am admittedly poorly describing?

Thanks,
Jim
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Old October 19th, 2008, 12:54   #14
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Jim, are you meaning the N-18 solenoid for the EGR?
The N75 drives the turbo controls.

Your MAF readings at low power and idle are what I would expect with the N-18 not working, and the EGR stuck closed, so that does jive.

A bad N18 is supported by the test information you gave.

Find the N18 and the N75, and verify the N-18 solenoid is electrically plugged in. It would be embarrasing if it had just come unplugged.

Dan
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Old October 19th, 2008, 14:34   #15
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Did I say N75? Of course I meant N18

I will take a closer look at the connection. When I checked the vacuum lines it wasn't hanging off or anything like that.
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